Re: [Qemu-devel] [Qemu-block] New iotest repros failures on virtio external snapshot with iothread

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Apr 04, 2017 at 03:13:44PM +0100, Alex Bennée wrote:
> 
> Stefan Hajnoczi <stefanha@gmail.com> writes:
> 
> > On Wed, Mar 29, 2017 at 07:01:38PM -0700, Ed Swierk wrote:
> >> Parts of qemu's block code have changed a lot in recent months but are
> >> not well exercised by current tests.
> <snip>
> >
> > 4. How to automate tests with real Linux guests?  This is a complex
> > topic and probably what we should discuss in this email thread.
> >
> > The buildroot + busybox approach is good for a small set of sanity
> > tests.  There was a similar attempt here:
> > https://github.com/stsquad/qemu-jeos
> >
> > Building from source becomes a challenge when other people want to add
> > software to test other areas of QEMU.  The process also requires
> > attention to maintain the image over time (e.g. as host build
> > environments change).
> >
> > There are image builder tools like virt-builder and mkosi for building
> > bootable virtual machine images based on standard Linux distros:
> > http://libguestfs.org/virt-builder.1.html
> > https://github.com/systemd/mkosi
> >
> > This eliminates the build-from-source hassles and gives us a full Linux
> > guest environment.  Booting is very fast with mkosi so the advantage to
> > custom building a minimal image is negligible.
> 
> Does it entirely? If your building a ARM guest on x86 how do you ensure
> the cross-compilers are correct for the kernel and userspace?

virt-builder and mkosi install binary distros like Debian or Fedora.
They do not compile from source.

virt-builder supports cross-arch image building so it's a good starting
point for QEMU guest images.

> > My suggestion is:
> >
> > Let's pick an image builder tool like virt-builder and keep a single
> > build script per guest architecture (e.g.  build-test-os-x86_64.sh).
> > All tests for that architecture run against the same disk image.
> >
> > It's easy to add additional software to the disk image by modifying the
> > build script.
> >
> > A Makefile ensures that the image file gets rebuilt if the build script
> > has changed.
> 
> I have experimented building LTP for foreign guests inside docker
> images. I expect the docker build image could be extended to build full
> kernel and file-systems in a known environment, possibly using
> virt-builder to do it.

My concern with building from source is that extending and maintaining
the infrastructure does not scale.  These efforts fizzle out like
qemu-jeos because no one really has time to maintain them.  Few people
want to extend them because they are complex and brittle.

Image builder tools skip the complexity of build-from-source.  You start
with something like a Dockerfile or virt-builder command-line.  It's
much easier for people to contribute and there is much less that can go
wrong at image build time.

Stefan

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